netdev - Re: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs with TCQ_F

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Date:	Thu, 25 Sep 2014 08:05:38 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Toke Høiland-Jørgensen <toke@...e.dk>,
	Florian Westphal <fw@...len.de>,
	Dave Taht <dave.taht@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [net-next PATCH 1/1 V4] qdisc: bulk dequeue support for qdiscs
 with TCQ_F_ONETXQUEUE

On Thu, Sep 25, 2014 at 7:57 AM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
> On Thu, 25 Sep 2014 07:40:33 -0700
> Tom Herbert <therbert@...gle.com> wrote:
>
>> A few test results in patch 0 are good. I like to have results for
>> with and without patch. These should two things: 1) Any regressions
>> caused by the patch 2) Performance gains (in that order of importance
>> :-) ). There doesn't need to be a lot here, just something reasonably
>> representative, simple, and should be easily reproducible. My
>> expectation in bulk dequeue is that we should see no obvious
>> regression and hopefully an improvement in CPU utilization-- are you
>> able to verify this?
>
> We are saving 3% CPU, as I described in my post with subject:
> "qdisc/UDP_STREAM: measuring effect of qdisc bulk dequeue":
>  http://thread.gmane.org/gmane.linux.network/331152/focus=331154
>
> Using UDP_STREAM on 1Gbit/s driver igb, I can show that the
> _raw_spin_lock calls are reduced with approx 3%, when enabling
> bulking of just 2 packets.
>
That's great. In commit log, would be good to have results with
TCP_STREAM also and please report aggregate CPU utilization changes
(like from mpstat).

Thanks,
Tom

> This test can only demonstrates a CPU usage reduction, as the
> throughput is already at maximum link (bandwidth) capacity.
>
> Notice netperf option "-m 1472" which makes sure we are not sending
> UDP IP-fragments::
>
>  netperf -H 192.168.111.2 -t UDP_STREAM -l 120 -- -m 1472
>
> Results from perf diff::
>
>  # Command: perf diff
>  # Event 'cycles'
>  # Baseline  Delta    Symbol
>  # no-bulk   bulk(1)
>  # ........  .......  .........................................
>  #
>      7.05%   -3.03%  [k] _raw_spin_lock
>      6.34%   +0.23%  [k] copy_user_enhanced_fast_string
>      6.30%   +0.26%  [k] fib_table_lookup
>      3.03%   +0.01%  [k] __slab_free
>      3.00%   +0.08%  [k] intel_idle
>      2.49%   +0.05%  [k] sock_alloc_send_pskb
>      2.31%   +0.30%  netperf  [.] send_omni_inner
>      2.12%   +0.12%  netperf  [.] send_data
>      2.11%   +0.10%  [k] udp_sendmsg
>      1.96%   +0.02%  [k] __ip_append_data
>      1.48%   -0.01%  [k] __alloc_skb
>      1.46%   +0.07%  [k] __mkroute_output
>      1.34%   +0.05%  [k] __ip_select_ident
>      1.29%   +0.03%  [k] check_leaf
>      1.27%   +0.09%  [k] __skb_get_hash
>
> A nitpick is that, this testing were done on V2 of the patchset.
>
> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Sr. Network Kernel Developer at Red Hat
>   Author of http://www.iptv-analyzer.org
>   LinkedIn: http://www.linkedin.com/in/brouer
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